On Fri, Sep 6, 2013 at 5:51 PM, Simon Davies <simon.james.dav...@gmail.com>wrote:
> On 6 September 2013 16:38, Pepijn Van Eeckhoudt <pep...@vaneeckhoudt.net> > wrote: > > Hi, > > > > In the extension I'm developing (https://bitbucket.org/luciad/libgpkg) > > I'm currently adding support for queries like: > > select Distance( > > GeomFromText('Point(13.457 3)'), > > geometry > > ) from table; > > > > GeomFromText takes a string and outputs a geometry blob > > Distance takes two geometry blobs and returns a double > > > > In order to speed up the distance function I was wondering if I could > > use aux_data to cache the parsed version of the first parameter since > > this remains the same for every call. So far I haven't been able to get > > this to work though, aux_data is always NULL, no matter what I try. > > > > My hunch is that this is because the first parameter is the result of a > > function call which could in theory return different values for each row > > even if the input parameters are constant. Is that correct? > > > > Are there any other ways to kind of memoize the GeomFromText function > > (or the parameters to distance) besides aux_data? > > select Distance( constGeom, geometry ) from table, (select > GeomFromText('Point(13.457 3)') as constGeom ); > Clever. Thanks for that. Or make your Distance function implementation do the GeomFromText implicitly, with a bit of duck-typing. You can test the argument's type, if blob use it as-is (hoping it's a "geometry" blob in all cases), and if text, do the GeomFromText() implicitly. Since it's back to being a (text) constant, you can use aux_data again. --DD _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
